GODRIVER-2806: Implement automatic GCP token acquisition (#1708)

Co-authored-by: Matt Dale <9760375+matthewdale@users.noreply.github.com>

Author: pmeredit

.evergreen/config.yml

@@ -2000,6 +2000,31 @@ tasks:
           export AZUREOIDC_TEST_CMD="PROJECT_DIRECTORY='.' OIDC_ENV=azure OIDC=oidc ./etc/run-oidc-test.sh ./test"
           bash $DRIVERS_TOOLS/.evergreen/auth_oidc/azure/run-driver-test.sh
 
+  - name: "oidc-auth-test-gcp-latest"
+    commands:
+    - command: shell.exec
+      params:
+        working_dir: src/go.mongodb.org/mongo-driver
+        shell: bash
+        script: |-
+          set -o errexit
+          ${PREPARE_SHELL}
+          export GCPOIDC_DRIVERS_TAR_FILE=/tmp/mongo-go-driver.tar.gz
+          # we need to statically link libc to avoid the situation where the VM has a different
+          # version of libc
+          go build -tags osusergo,netgo -ldflags '-w -extldflags "-static -lgcc -lc"' -o test ./cmd/testoidcauth/main.go
+          rm "$GCPOIDC_DRIVERS_TAR_FILE" || true
+          tar -cf $GCPOIDC_DRIVERS_TAR_FILE ./test
+          tar -uf $GCPOIDC_DRIVERS_TAR_FILE ./etc
+          rm "$GCPOIDC_DRIVERS_TAR_FILE".gz || true
+          gzip $GCPOIDC_DRIVERS_TAR_FILE
+          export GCPOIDC_DRIVERS_TAR_FILE=/tmp/mongo-go-driver.tar.gz
+          # Define the command to run on the gcp VM.
+          # Ensure that we source the environment file created for us, set up any other variables we need,
+          # and then run our test suite on the vm.
+          export GCPOIDC_TEST_CMD="PROJECT_DIRECTORY='.' OIDC_ENV=gcp OIDC=oidc ./etc/run-oidc-test.sh ./test"
+          bash $DRIVERS_TOOLS/.evergreen/auth_oidc/gcp/run-driver-test.sh
+
   - name: "test-search-index"
     commands:
       - func: "bootstrap-mongo-orchestration"
@@ -2342,6 +2367,30 @@ task_groups:
     tasks:
       - oidc-auth-test-azure-latest
 
+  - name: testgcpoidc_task_group
+    setup_group:
+      - func: fetch-source
+      - func: prepare-resources
+      - func: fix-absolute-paths
+      - func: make-files-executable
+      - command: subprocess.exec
+        params:
+          binary: bash
+          env:
+            AZUREOIDC_VMNAME_PREFIX: "GO_DRIVER"
+          args:
+            - ${DRIVERS_TOOLS}/.evergreen/auth_oidc/gcp/setup.sh
+    teardown_task:
+      - command: subprocess.exec
+        params:
+          binary: bash
+          args:
+            - ${DRIVERS_TOOLS}/.evergreen/auth_oidc/gcp/teardown.sh
+    setup_group_can_fail_task: true
+    setup_group_timeout_secs: 1800
+    tasks:
+      - oidc-auth-test-gcp-latest
+
   - name: test-aws-lambda-task-group
     setup_group:
       - func: fetch-source
@@ -2693,3 +2742,5 @@ buildvariants:
         batchtime: 20160 # Use a batchtime of 14 days as suggested by the CSFLE test README
       - name: testazureoidc_task_group
         batchtime: 20160 # Use a batchtime of 14 days as suggested by the CSFLE test README
+      - name: testgcpoidc_task_group
+        batchtime: 20160 # Use a batchtime of 14 days as suggested by the CSFLE test README

cmd/testoidcauth/main.go

@@ -91,6 +91,8 @@ func main() {
 	case "azure":
 		aux("machine_5_1_azureWithNoUsername", machine51azureWithNoUsername)
 		aux("machine_5_2_azureWithNoUsername", machine52azureWithBadUsername)
+	case "gcp":
+		aux("machine_6_1_gcpWithNoUsername", machine61gcpWithNoUsername)
 	default:
 		log.Fatal("Unknown OIDC_ENV: ", env)
 	}
@@ -736,3 +738,23 @@ func machine52azureWithBadUsername() error {
 	}
 	return nil
 }
+
+func machine61gcpWithNoUsername() error {
+	opts := options.Client().ApplyURI(uriSingle)
+	if opts == nil || opts.Auth == nil {
+		return fmt.Errorf("machine_6_1: failed parsing uri: %q", uriSingle)
+	}
+	client, err := mongo.Connect(context.Background(), opts)
+	if err != nil {
+		return fmt.Errorf("machine_6_1: failed connecting client: %v", err)
+	}
+	defer client.Disconnect(context.Background())
+
+	coll := client.Database("test").Collection("test")
+
+	_, err = coll.Find(context.Background(), bson.D{})
+	if err != nil {
+		return fmt.Errorf("machine_6_1: failed executing Find: %v", err)
+	}
+	return nil
+}

x/mongo/driver/auth/oidc.go

@@ -10,6 +10,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"io"
 	"net/http"
 	"net/url"
 	"strings"
@@ -174,12 +175,12 @@ func (oa *OIDCAuthenticator) providerCallback() (OIDCCallback, error) {
 			return nil, newAuthError(fmt.Sprintf("%q must be specified for Azure OIDC", resourceProp), nil)
 		}
 		return getAzureOIDCCallback(oa.userName, resource, oa.httpClient), nil
-	// TODO GODRIVER-2806: Automatic token acquisition for GCP Identity Provider
-	// This is here just to pass the linter, it will be fixed in one of the above tickets.
 	case gcpEnvironmentValue:
-		return func(ctx context.Context, args *OIDCArgs) (*OIDCCredential, error) {
-			return nil, fmt.Errorf("automatic token acquisition for %q not implemented yet", env)
-		}, fmt.Errorf("automatic token acquisition for %q not implemented yet", env)
+		resource, ok := oa.AuthMechanismProperties[resourceProp]
+		if !ok {
+			return nil, newAuthError(fmt.Sprintf("%q must be specified for GCP OIDC", resourceProp), nil)
+		}
+		return getGCPOIDCCallback(resource, oa.httpClient), nil
 	}
 
 	return nil, fmt.Errorf("%q %q not supported for MONGODB-OIDC", environmentProp, env)
@@ -228,6 +229,37 @@ func getAzureOIDCCallback(clientID string, resource string, httpClient *http.Cli
 	}
 }
 
+// getGCPOIDCCallback returns the callback for the GCP Identity Provider.
+func getGCPOIDCCallback(resource string, httpClient *http.Client) OIDCCallback {
+	// return the callback parameterized by the clientID and resource, also passing in the user
+	// configured httpClient.
+	return func(ctx context.Context, args *OIDCArgs) (*OIDCCredential, error) {
+		resource = url.QueryEscape(resource)
+		uri := fmt.Sprintf("http://metadata/computeMetadata/v1/instance/service-accounts/default/identity?audience=%s", resource)
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, uri, nil)
+		if err != nil {
+			return nil, newAuthError("error creating http request to GCP Identity Provider", err)
+		}
+		req.Header.Add("Metadata-Flavor", "Google")
+		resp, err := httpClient.Do(req)
+		if err != nil {
+			return nil, newAuthError("error getting access token from GCP Identity Provider", err)
+		}
+		defer resp.Body.Close()
+		if resp.StatusCode != http.StatusOK {
+			return nil, newAuthError(fmt.Sprintf("failed to get a valid response from GCP Identity Provider, http code: %d", resp.StatusCode), nil)
+		}
+		accessToken, err := io.ReadAll(resp.Body)
+		if err != nil {
+			return nil, newAuthError("failed parsing reading response from GCP Identity Provider", err)
+		}
+		return &OIDCCredential{
+			AccessToken: string(accessToken),
+			ExpiresAt:   nil,
+		}, nil
+	}
+}
+
 func (oa *OIDCAuthenticator) getAccessToken(
 	ctx context.Context,
 	conn driver.Connection,